Waiting Times
[Pages:38]Waiting Times
Chapter 7
These slides are based in part on slides that come with Cachon & Terwiesch book Matching Supply with Demand . If you want to use these in your course, you may have to adopt the book as a textbook
or obtain permission from the authors Cachon & Terwiesch. 1
utdallas.edu/~metin
Learning Objectives
Interarrival and Service Times and their variability Obtaining the average time spent in the queue Pooling of server capacities Priority rules
utdallas.edu/~metin
2
Where are the queues?
utdallas.edu/~metin
3
A Queue is made of a server and a queue in front
Input:
Passengers in an airport Customers at a bank Patients at a hospital Callers at a call center
Arrival rate
Buffer
Queues
Processing
Resources:
Check-in clerks at an airport Tellers at a bank Nurses at a hospital Customer service representatives
(CRS) at a call center
Capacity
We are interested in the waiting times in the queue and the queue length.
utdallas.edu/~metin
An Example of a Simple Queuing System
Incoming calls
Calls on Hold
Reps processing
calls
Answered Calls
Call center
Blocked calls (busy signal)
Abandoned calls (tired of waiting)
At peak, 80% of calls dialed received a busy signal.
Customers getting through had to wait on average 10 minutes
Extra phone line expense per day for waiting was $25,000.
Financial consequences
Lost throughput
utdallas.edu/~metin
Holding cost Lost goodwill Lost throughput (abandoned)
Cost of capacity Cost per customer
$$$ Revenue $$$
5
A Somewhat Odd Service Process
Constant Arrival Rate (0.2/min) and Service Times (4 min)
Arrival rate 0.2/min = 1/(4 mins) = 1 every five minutes, which implies interarrival time of 5 minutes. Units of arrival rate 1/min whereas units of interarrival time is min.
Arrival Service
Patient Time
Time
1
0
4
2
5
4
3
10 4
4
15 4
5
20 4
6
25 4
7
30 4
8
35 4
9
40 4
10 45 4
11 50 4
12 55 4
utdallas.edu/~metin
7:00
7:10
7:20
7:30
7:40
7:50
8:00 6
Where is Variability?
There certainly is significant (actually infinite) amount of waiting when the arrival rate is greater than the service rate
? Equivalently, the processing capacity is less than the arrival rate
More interestingly, variability can cause long waiting times. Variability in
? Arrival process ? Processing times ? Availability of resources; Absent, sick, broken or vacationing servers. ? Types of customers; Priority versus regular customers. ? Routing of flow units; Recall the Resume Validation Example. ? Response of customers to waiting for a while; Wait more or abandon
utdallas.edu/~metin
7
Variability: Where does it come from? Examples
Tasks:
? Inherent variation ? Lack of Standard Operating Procedures ? Quality (scrap / rework)
Input:
Buffer
? Unpredicted Volume swings
? Random arrivals (randomness is the rule,
not the exception)
? Incoming quality
? Product Mix
Especially relevant in service operations (what is different in service industries?): ? emergency room ? air-line check in ? call center ? check-outs at cashier
utdallas.edu/~metin
Processing
Resources:
? Breakdowns / Maintenance ? Operator absence ? Set-up times
Routes:
? Variable routing ? Dedicated machines
................
................
In order to avoid copyright disputes, this page is only a partial summary.
To fulfill the demand for quickly locating and searching documents.
It is intelligent file search solution for home and business.
Related searches
- bcps magnet program waiting list
- va irrl waiting period 2019
- open section 8 waiting list
- open public housing waiting lists
- section 8 housing waiting list
- housing waiting list open
- cd waiting period trid
- baltimore county magnet school waiting list
- still waiting for my refund
- waiting line synonym
- another word for waiting line
- word for waiting for something